| Laosaurus | |
|---|---|
 | |
| Pubis ofLaosaurus (unknown species; possiblyL. celer) in 1896 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Neornithischia |
| Genus: | †Laosaurus Marsh,1878 |
| Type species | |
| †Laosaurus celer | |
| Species | |
| |
Laosaurus (meaning "stone orfossil lizard") is agenus ofneornithischiandinosaur. The type species,Laosaurus celer, was first described byO.C. Marsh in 1878 from remains from theOxfordian-Tithonian-ageUpper JurassicMorrison Formation ofWyoming. The validity of this genus is doubtful because it is based on fragmentary fossils. A second species from the Morrison Formation,L. gracilis, and a species from thelate CretaceousAllison Formation ofAlberta,Canada,Laosaurus minimus, are also considereddubious.
Marsh (1878a) named his new genus fromvertebrae (YPM 1874) found bySamuel Wendell Williston atComo Bluff,Wyoming, from rocks of theMorrison Formation. Thetype material includes nine partial and two complete tailvertebral centra, which he concluded came from a "fox-sized" animal.[1] In the same year, he named two other species:L. gracilis, originally based on a back vertebral centrum, a tail vertebral centrum, and part of anulna;[1][2] andL. altus, originally based on apelvis, hindlimb, and tooth (YPM 1876).[3] A review byPeter Galton in 1983 found the type ofL. gracilis to consist of thirteen back and eight tail centra, and portions of both hindlimbs.[4]Charles Gilmore had assigned additional remains, including a partial skeleton (CM 11340), toL. gracilis based on size,[5][6] but Galton transferred the remains to other taxa, assigning the skeleton toDryosaurus.[4]Marsh returned to the genus in 1894, when additional remains convinced him thatL. altus deserved its own genus (Dryosaurus), and that there was another species present:L. consors, based on YPM 1882, a partial skeleton also from Como Bluff.[7] In 1895, he coined the family Laosauridae for his genus, but this was eventually considered synonymous withHypsilophodontidae.[8]
Charles Gilmore in 1909 assigned a juvenilefemur (USNM 5808) toL. gracilis,[5] and in 1925 added partial skeleton CM 11340 toL. gracilis, based on size,[6] but Galton transferred the femur toOthnielia (nowNanosaurus) and the skeleton toDryosaurus in 1983. Gilmore also described the fifth and final species,L. minimus (species name for its small size), based onNMC 9438, a partial left hindlimb and vertebral bits from theLate Cretaceous (late Campanian)Allison Formation ofAlberta,Canada.[9] At the time, though, the discovery locality was thought to be in theEarly CretaceousBlairmore Group, but fieldwork at theL. minimus type locality in the early 1930s showed it to be within theBelly River Group, andLoris Russell published a paper in 1949 recognizing this new geologic information, while finding it generically distinct fromLaosaurus proper.[10] Russell found this taxon to be most likeHypsilophodon, from the Early CretaceousWessex Formation of southernEngland.[10]
The next major publications which mentionedLaosaurus prominently were by Galton. In 1977, he assignedL. consors andL. gracilis to his newtaxonOthnielia rex;[11] and in 1983 he redescribed most of the material and reassigned some of it, as described above.[4] Galton (1983) is also one of the sources for the "Troodon ascarnivorousornithopod"hypothesis of the early 1980s, because it assignsL. minimus toTroodon, based on unpublished evidence.[4] This would tie in with theOrodromeus/Troodonegg confusion of a few years later, which was eventually settled asTroodon individuals eatingOrodromeus individuals at their nesting site (thetroodontidembryoes were confused with hypsilophodont embryoes).[12]L. celer was assessed as dubious by Galton, a status it has kept through the last major reviews.[13][14]
Two further developments have occurred. First,L. minimus is seen as a possible second species or specimen ofOrodromeus (Sues and Norman, 1990),[verification needed] although the remains are too meager to be certain.[13] Second, Galton, in a 2007 review, declaredOthnielia rex to be based on undiagnostic remains, and shifted diagnostic referred remains to new taxonOthnielosaurus consors, a new combination based on the originalL. consors partial skeleton.[15]
